Berliner-Joyce XP-13 Viper

Last revised June 7, 1998

The XP-13 Viper was the last fighter built by the Thomas-Morse
Aircraft Corporation of Ithaca, New York. The Thomas-Morse Aircraft
Corporation had started life in early 1917 when the Thomas Brothers
Aeroplane Company merged with the Morse Chain Works. The Thomas-Morse
outfit built the well-known S-4 fighter-trainer of World War 1, which
never actually served in combat, but became a very popular participant
at postwar air shows. They also designed and developed the MB-3, the
first American fighter of indigenous design to enter service.
However, under the bizarre military procurement policy of the early
1920s, Boeing actually obtained the bulk of the production contracts
for the MB-3. During the 1920s, Thomas-Morse specialized in the
construction of all-metal designs, observation planes, and racers,
although a few unsuccessful fighter projects were attempted. Like
lots of other companies, Thomas-Morse found that firm military orders
were hard to come by.

The XP-13 (named "Viper" by the company) was created for the new 600
hp Curtiss H-1640-1 Chieftain twelve-cylinder 2-row air cooled engine.
Thomas-Morse's experience with the manufacture of all-metal aircraft
stood them in good stead in the design of the Viper. The fuselage had
an all-metal structure covered by a corrugated aluminum-sheet skin.
The wing was of wooden construction with fabric covering, but the
ailerons were made of corrugated metal sheet. Tail surfaces were of
metal and fabric, but the control surfaces were covered with
corrugated sheet metal.

The Viper was delivered to the USAAC for evaluation in early 1929.
The aircraft was tested at Wright Field in June 1929 as P-559, then
purchased by the Army and designated XP-13. The serial number was
29-453. Performance was satisfactory, but the Chieftain suffered
with insurmountable cooling problems. Similar problems had been
encountered with Curtiss-built fighters powered by this engine. The
XP-13 had an empty weight of 2262 lbs and a gross weight of 3256 lb.
The maximum speed was 172.5 mph at sea level, 169.9 mph at 5000 feet.
The XP-13 could climb to 5000 feet in 3 minutes, and the service
ceiling was 20,800 feet. The XP-13 was not fitted with any armament.

Because of the insoluble overheating problems, the Chieftain engine
was abandoned. The XP-13 prototype then had a new engine installed in
September 1930, a 525 hp Pratt and Whitney SR-1340-C enclosed in a
NACA cowling, along with a revised fin and rudder. The designation
was changed to XP-13A. The change to a new engine resulted in even
better performance. The XP-13A had an empty weight of 2224 lbs and a
gross weight of 3194 lb. Maximum speed was 188.5 mph at 5000 feet.
The XP-13A could climb to 5000 feet in 3.5 minutes, and service
ceiling was 24,150 feet. A USAAC performance report of 1930 described
the XP-13A as having a "comfortable feel" in all aerobatics and that
it "makes a wonderfully smooth slow roll". However, by then the
opportunity was lost. and the Army never ordered the aircraft into
production. The Viper caught fire during its last test flight and was
destroyed in the resulting crash.

A second Viper was to have been built by Curtiss under the designation
XP-14. However, the failure of the Chieftain engine was to cause this
project to be cancelled before any aircraft could be built.

The failure of the XP-13 to win a contract was catastrophic for the
Thomas-Morse company. In August, 1929, the Thomas-Morse company was
taken over by the Consolidated Aircraft Company of Buffalo, New York.
The Thomas-Morse company disappeared as a separate entity shortly
thereafter.

Sources:

United States Military Aircraft Since 1909, Gordon Swanborough and Peter Bowers, Smithsonian Institution Press, 1989.